In general, centrifuge devices and methods designed to separate finely divided particulate material from suspending liquid are well-known. Such devices and methods have been utilized for the separation of solid blood components from whole blood or from a liquid blood fraction. While the present invention has broader utility than the separation of blood components, the invention will be illustrated in terms of embodiments relating to the separation of solid blood components.
Advances in assay techniques and analytical instrumentation has made it possible to carry out a variety of hematological, chemical and toxicological diagnostic procedures on very small quantities of blood. This offers a tremendous advantage since it obviates the need and skill required to withdraw veinuous blood from a patient. Instead, sufficient quantities of blood can now be obtained by the less traumatic procedure of collecting capillary source blood from a fingertip, ear lobe or the like.
Of particular interest are blood tests including glucose, LDH, SGOT, SGPT, BUN, total protein, phosphatase, bilirubin, calcium, chloride, sodium, potassium, and magnesium. Since such tests are normally performed on blood plasma, blood cells should be removed from whole blood samples and the platelets should be reduced prior to analysis.
Typically, however, devices designed for fractionation and separation of cellular components from whole blood tend to be mechanically complicated, expensive, inefficient and difficult to clean or sterilize for use. Another difficulty with known centrifuge devices or methods is the time required to effect the separation of solid particulate material suspended in a liquid. In many diagnostic tests performed in a physician's office it is important to have a volume of plasma or serum from a sample of blood in as short a time as possible. To be able to give the results of office testing to the patient such testing must be completed within 10 to 15 minutes. Any longer period of time results in prolonged waiting for the patient and overcrowding of the physician's office. Typically, centrifuging techniques require about 10 minutes of spin time. This does not permit effective diagnostic testing in the physician's office. Accordingly, apparatus and a method are needed to allow much more rapid plasma or serum separation to be effected at low cost.
In U.S. Pat. No. 3,957,653 apparatus for collection, separation and isolation of blood is disclosed comprising a test tube in which blood sample is introduced. Each test tube has a complicated closure member which provides a hermetic seal of the contents within the test tube. According to the indicated procedure blood in the test tube is centrifuged to effect removal of thixotrope which passes through an aperture into a chamber present in the closure member. The thixotropic material flows under centrifugal stress to its density gradient level between the blood components where it comes to rest and then assumes a rigid thixotropic structure which acts as a barrier between the separated blood components. Not only is the structure of the disclosed apparatus complicated, but it is expensive to manufacture and requires a density gradient level to equilibrate between the blood components in order to achieve the desired separation. Accordingly, the procedure is time consuming and not an effective means of separating components of blood.
U.S. Pat. No. 4,509,941 discloses a centrifuge device having a liner composed of porous material for entrapping solid particles during rotation of the centrifuge device. While this particular centrifuge device is effective it tends to be expensive because of the need for multiple parts and the necessity for assembling these multiple parts. Moreover, the nature of the liner material is a limiting factor in the effectiveness of the device. The liner used to entrap solid particles which are present in a suspending liquid limits the usefulness of the device in that as soon as the fractionation procedure begins the liner designed to entrap solid particles become less and less receptive to entrapping additional particles.
The present invention is directed to a disposable, low cost device which effectively separates solid particulate materials suspended in a liquid very rapidly. The system is easy to use and can be operated by a technician or unskilled lay person.